1. Field of the Invention
The present invention relates to a liquid crystal display apparatus which employs a ferroelectric liquid crystal and, more particularly, to a liquid crystal display apparatus which performs display with gradation control.
2. Description of the Related Art
Japanese Patent Laid-Open Publication No. 61-94023 discloses a display apparatus which employs a ferroelectric liquid crystal. More particularly, this liquid crystal display apparatus employs a pair of glass substrates which are provided with transparent electrodes on their inner surfaces and which have been subjected to an orientation or alignment treatment. The glass substrates are disposed to oppose each other leaving therebetween a gap of 1 to 3 microns. The gap is filled with a ferroelectric liquid crystal.
A liquid crystal display device employing a ferroelectric liquid crystal is conveniently switched by a combination of an external electric field and spontaneous polarization possessed by the ferroelectric liquid crystal. In addition, switching can easily be effected by changing the polarity of the external electric field by virtue of the fact that the direction of the longer axes of the ferroelectric liquid crystal molecules corresponds to the direction of the spontaneous polarization.
On the other hand, various liquid crystal display devices using chiral smectic liquid crystal are disclosed in the following United States Patents: U.S. Pat. Nos. 4,639,089; 4,681,404; 4,682,858; 4,709,994; 4,712,872; 4,712,873; 4,712,874; 4,712,875; 4,721,367; 4,728,176; 4,740,060; 4,744,639; 4,747,671; 4,763,992; 4,773,738; 4,776,676; 4,778,259; 4,783,148; 4,796,979; 4,800,382; 4802,740; 4,818,075; 4,818,078; 4,820,026; 4,836,656; 4,844,590; 4,869,577, 4,878,740; 4,879,059; 4,898,456; 4,907,859; 4,917,471; 4,932,757; 4,932,758; 5,000,545; 5,007,716; 5,013,137; 5,026,144; 5,054,890; and 5,078,475.
In general, however, chiral smectic liquid crystal has a bi-stable characteristic, so that it has been difficult to display an image with gradation control by using this type of liquid crystal.